The interpretation of the ultrafast photophysics of transition metal complexes following photoabsorption is quite involved as the heavy metal center leads to a complicated and entangled singlet-triplet manifold. This opens...

To understand the effect of structural rigidity or flexibility on the intersystem crossing rate, herein we have adopted time dependent correlation function based approach, an exact method for harmonic oscillator...

We demonstrate that spin-vibronic coupling is the most significant mechanism in vibrational coherence transfer (VCT) from the singlet (S 1 ) to the triplet (T 1 ) state of the [Pt 2 (P 2 O 5 H 2 ) 4 ] 4− complex. Our time-dependent correlation function-based study shows that the rate of intersystem crossing (k ISC ) through direct spin−orbit coupling is negligibly small, making VCT vanishingly small due to the ultrashort decoherence time (2.5 ps). However, the inclusion of the spin-vibronic contribution to the net k ISC in selective normal modes along the Pt−Pt axis increases the k ISC to such an extent that VCT becomes feasible. Our results suggest that k ISC for the S 1 →T 2 (τ ISC = 1.084 ps) is much faster than the S 1 → T 1 (τ ISC = 763.4 ps) and S 1 → T 3 (τ ISC = 13.38 ps) in CH 3 CN solvent, indicating that VCT is possible from the low-lying excited singlet (S 1 ) to the triplet (T 1 ) state through the intermediate T 2 state. This is the first example where VCT occurs solely due to spin-vibronic interactions. This finding can pave the way for new types of photocatalysis.

We highlight the important roles the direct spin-orbit coupling (DSO), the spin-vibronic coupling (SV) and the dielectric constant of the medium play on the reverse intersystem crossing (RISC) mechanism of TXO-TPA and TXO-PhCz molecules. To understand this complex phenomenon, we have calculated the RISC rate constant, kRISC, using a time-dependent correlation function-based method within the framework of second-order perturbation theory. Our computed kRISC in two different solvents, toluene and chloroform, suggests that in addition to the DSO, a dielectric medium-dependent SV mechanism may also has a significant impact on the net enhancement of the rate of RISC from the lowest triplet state to the first excited singlet state. Whereas we have found that kRISC of TXO-TPA is mostly determined by the DSO contribution independent of the choice of solvent, the SV mechanism contributes more than 30 percent to the overall kRISC of TXO-PhCz in chloroform. In toluene, however, the SV mechanism is less important for the RISC process of TXO-PhCz. An analysis of mode-specific nonadiabatic coupling (NAC) between T2-T1 of TXO-PhCz and TXO-TPA suggests that the NAC values in certain normal modes of TXO-PhCz are much higher than that of TXO-TPA and it is more pronounced with chloroform as a solvent. The findings demonstrate the role of the solvent-assisted SV mechanism towards the net RISC rate constant, which in turn maximizes the efficiency of thermally activated delayed fluorescence.

We present a composite framework for calculating the rate of non-radiative deactivation processes, namely internal conversion (IC) and intersystem crossing (ISC), on an equal footing by explicitly computing the non-adiabatic...